Control mechanism



Jan. 18, 1944. E. M. LONG CONTROLv MECHANISM 2 Shets-Sheet 1 Filed Jan. 21 1942 50 IHVENTUR FL! MLDNG' IEIY Z AT BRHEY Jan. 18, 1944. E. M. LONG I zgams CONTROL MECHANISM Filed Jan. 21, 1942 2 Sheets-Shegt 2 INVENTIJ ATT CIRNET ELI MLUNG.

Patented Jan. 18, 1944 UNITED STAT ATENT OFFICE 2,339,708 CONTROL MECHANISM.

Application January 21, 1942, Serial No. 427,675

9 Claims.

This invention relates to improvements in a control mechanism for adjusting certain parts of a machine with respect to other parts thereof, and for releasably maintainin the same in the adjusted position.

One of the objects of this invention is to produce an improved manually operated control mechanism which is peculiarly adapted to be used in connection with the grinding couple of a lens grinding and polishing machine for maintaining a lens and the grinding surface of a grinding couple, comprising a work holder and a grinding tool or lap, in predetermined pressure engagement with each other while the machine is in operation.

Another object of the invention resides in providin a control device of the above mentioned character which is so constructed and operated that micrometric or infinite adjustment of the device may be obtained either prior to the operation of a machine with which it is associated or at any time during such operation for producing and maintaining a predetermined relation between relatively movable parts of said machine.

A further object of the invention is to provide produce a control mechanism ,or unit of the above mentioned character which is durable and economical in construction and which is simple and positive in operation.

Other objects and advantages pertaining to the specific construction of my control device and to the form and relation of the parts thereof will more fully appear from the following description taken in conjunction with the accompanying drawings in which:

Figure l is a detail side elevation showing a portion of a lens grindin machine and a control mechanism associated therewith embodying the various features of this invention, portions of the control mechanism being shown broken away and in section.

Figure 2 is a front elevation of the mechanism illustrated in Figure 1.

Figure 3 is a detail vertical sectional view taken on line 33, Figure 1, showing a cross section of the brake mechanism incorporated in my control device for releasably maintaining the device in an adjusted position.

Figur @l is a detail side elevation illustrating a modified form of lever mechanism comprising a portion of my control device by which the same may be actuated.

Figures5, 6 and 7 are views similar to Figure 4 illustrating further modified forms oi lever mechanism by which my cont o c rn cs ureappl ine device may be actuated.

Figure 8 i a detail horizontal sectional view taken on line 8-3, Figure 7, g

The machine which I have indicated in the rawin s fo llu rat ng a r ctica p c t f m c ntr l m cha m is on particu a ad pt f ri ding nd polish n th surf c s of toric lenses. Thi machine may be of any well known type ch as, cxam leithat sh and escr b d inr atent 1309,93 i sued April 1929. The m c ne oft at p tent ccmpri a pair of ri din and p is in c up es c3911 consisting of a work or lens holder and a grinding lap. The grinding lap is shown fixed to the frame of the machine, while the worlgiholder is actuated With respect to the lap by the combined a io f w l c p ccat mo em n s o erat n in di e t ons at substan al y ri t angles t each ct er- One ec ccati c m ent o era e s s a l r llel with the hasc x s c the lens bein g ound a d .is usua y called the enethwise rck Th o he ec n ccat c moveent e a sub tan ially paral el with the c lnd axi o the le nd s u u y alled the cross s roke 1 d r t ncr as t e efiic cncy o m ch nes o th ty e? continu us var ati n or break-up movement, sometimes called a third movement, may be introduced into either-or both of the reciprocative movementsso that the resultant path of movement of the movable element of the grinding and polishing couple 's a series of curvilinearstrokes and includes va large num of suc t c c be th movabkclce t com lete c c e o o erat o 9 r eat its pattern of movement.

.As show int c d in s 1.0 ind t aer ndng an l s i g ou le co p isin a Wcr 0 ns h de H an a g indin la 1 fihclap i2 s x y co ected y an suitalc c eans, u as a b ack t is, with the bas .9 rame '4 cf t e g d n machineh ice h l e h a i of c as l tice .1 atta he by .W pitch or the like thereto. ;,I;5 is alensactuating or press re arm wh c ma the c c c -b any abl m ch n m (pc shown. l unct cmn t pr duce tw rc i rcca vc Increment vore, 1= t ie at su tant a rie an e t ca i ptla icl moving t le s with res e to the lan- Th and tube normally urges said members apart.

The lower end of the tube 29 is provided with a pin 22 having a tapered end which rests in a suitable socket provided in the upper side of the arm I5 intermediate the pin I6 and the base I4. The upper end of the sleeve I9 is provided with a spherical member 23 which is loosely received in a suitable socket provided at the outer end of an arm 24 connected with a pressure head 25. The spring 2|, of course, tends to separate the telescoping members I9 and and in order that the spring will not move the members out of cooperative relation with each other a tie strap or cable 26 is attached at its lower end, as by a screw member 21, to the arm I5. The upper end of cable 26 is secured to a rod 28 which is slidably received in an aperture provided in the arm 24. The rod 28 has a collar 29 secured to the upper end thereof for limiting the downward movement of said rod. The sleeve I9, as shown in Figure 1, is provided with a laterally extending arm 39 which is bifurcated to receive the rod 23. The arm 39 and rod 28 maintain the sleeve I9 against rotary movement. The outer face of the sleeve I9 is provided with indicia 33 while the tube 29 is provided with an index 34, in the form of a colored ring or the like, adapted to appear through a slot 35 formed in the sleeve I9 and to register with the indicia 33 for indicating the amount of the pressure being applied to the arm I5, as shown in Figure 2.

The pressure head is provided with a bore 31 which slidably receives therein an upward extending hollow guide post 38 provided on a brake housing 39 secured by any suitable means tothe base 14. The head 25 is supported and positioned by an operating rod or positioning member 49 which extends upwardly from the housing 39 through guide post 38 and has the upper end thereof secured to the head by a nut M, as shown in Figure 1. The lower portion of the rod 40 is provided with rack teeth 43 in one side thereof which have meshing engagement with a pinion 44 mounted in the housing 39 between a pair of brake disks 45 and 46. These brake disks are rotatably mounted in recesses 41 and 48 respectively provided in the housing 39 at opposite sides thereof. The recesses 41 and 43 are substantially equal in depth to the thickness of the brake disks 45 and 46 so that the outer side surfaces of said disks are substantially flush with the corresponding sides of the housing 39 adjacent thereto. The pinion 44 is fixedly secured to one of the brake disks, as 45, in concentric relation therewith by screws 59 as illustrated in Figure 3." .The pinion 44 is provided with a central aperture having threads 5|. A screw shaft 52 extends through the central aperture in pinion and a corresponding aperture in brake disk 45 and is provided withthreads 53 engaging the th'eads' 5| in the pinion 44 so that upon relative rotary movement of the pinion 44 and shaft 52, saidlp'inion and shaft are moved axially with respect to one another. The brake disk 46 has a central aperture 55'which receives the adjacent end of the shaft 52 therein. The brake disk 46 is secured to the shaft 52 by a key 56 so as to rotate in unison with said shaft. A screw 51 mounted in the end of the shaft 52 holds the brake disk 45 on the shaft and provides for axial adjustment of the brake disk 46 with respect to the shaft and to the brake disk 45 secured to the pinion 44. The end of shaft 52 adjacent the brake disk 45 is provided with a substantially radially disposed handle 59 while a second handle 69 similar to the handle 59 is secured to the pinion 44 and brake disk 45 at one side of the center thereof. The handles 59 and 69 are arranged to lie substantially in a plane extending normal to the axis of the shaft 52 with the handle 60 normally arranged above and slightly spaced from the handle 59.

It will now be obvious that by moving the handles 59 and 69 toward or from each other a corresponding relative rotation of the shaft 52 and pinion 44 will be produced and by reason of the threaded or cam engagement of these actuating members will effect axial movement of the pinion 44 with respect to the shaft 52. The screw threads 5! and 53 are so arranged that when the handles 59 and 69 are moved away from each other, the resulting axial movement of the actuating members 44 and 52 moves the brake disks 45 and 46 inwardly toward one another. The brake disks are thus moved into frictional engagement with the inner end braking surfaces 41' and 48', respectively, of the recesses 41 and 48. When the handles 59 and 99 are moved toward each other, the brake disks 45 and 46 will, of

.course, be moved axially away from each other out of frictional holding engagement with the braking surfaces 41' and 48. In order that the brake disks will be norm-ally maintained in holding engagement with the braking surfaces 41 and 48', a spring 62 is interposed between the handles 59 and 69, as indicated in Figure 1, to yieldingly produce separation of the handles and consequent relative rotation of the actuating members 44 and 52 in the brake-applying direction.

It will now be observed that when it is desired to move the head 25 either up or down, it is only necessary to produce relative movement of the handles 59 and 60 toward each other against the action of the spring 62, thereby releasing the brake after which the arms. may be moved in unison in either direction, producing corresponding rotation in unison of the actuating members 44 and 52 and the brake disks 45 and 46. If greater pressure is to be produced between the work or lens L and the lap I2, the handles are moved downwardly or in an anticlockwise direction as viewed in Figure 1. This movement of the handles 59 and 99 rotates the pinion 44 in a direction to move the rod 40 and head 25 downwardly thereby forcing the sleeve I9 downwardly and thus increasing the pressure produced by spring 2! upon the tube 29 and arm I5. When the desired pressure is thus produced upon the arm I5, such pressure will be maintained until the handles are again moved about the axis of the shaft 52 due to the fact that as soon as said handles are released the spring 62 moves the handles away from each other and thereby effects holding engagement of the brake disks 45 and 49 with the braking surfaces 41' and 48. Furthermore, the force stored in spring 2| acts through the head 25 and rod 40 to rotate gear member 44 with respect to worm 53 in a direction to move brake disks 45 and 46 toward each other and engage the brake. The greater the pressure produced on arm I and the force stored in spring 2|, the tighter are the brake disks 45 and 46 engaged with the braking surfaces 47' and 48', and the greater will be the holding action of the brake. If, on the other hand, it is desired to lift the head and release the pressure on the arm [5, the handles 553 and 60 are moved upwardly or in a clockwise direction, as viewed in Figure 1, as soon as the brake has been released. This upward swinging movement of the handles produces a corresponding rotary movement of the pinion 44 and an upward vertical movement of the rack or rod member it. If the handles are moved sufficiently in a clockwise direction, the arm it will be lifted from operative engagement with the work or lens holder H by the cable 26. As soon as the handles are released, the brake, comprising the disks "i5 and 38 and braking surfaces 41' and t8, will again be engaged by the action of the spring 62 in the manner hereinbefore described. The arm l5 may'thus be maintained in its uppermost position out of engagement with the holder 5 i so that the holder and/ or lap being used may be exchanged for another one, or the work adjusted with respect to the holder.

The movement of the handles 59 and 6% toward each other may be produced by pressure applied to the outer surface of both handles, 01' it may be produced by pressure applied to the outer surface of either of these handles. It will thus be seen that in the structure shown in Figure 1, if it is desired to move the handles downwardly, it is only necessary to apply pressure to the upper surface of the handle as to move said handle in an anticlockwise direction. During the initial movement of the handle, the brake is disengaged after which both handles may move in unison to efiect rotation of the pinion 44 and the member, as the rod it, actuated thereby. If it is desired to move the handles in a clockwise direction, it is only necessary to apply pressure to the outer face of the handle 5!! to effect movement thereof in a clockwise direction. During the initial movement of the handle 59, the brake is disengaged after which the handles move in unison to effect rotation of the pinion 44 in a clockwise direction.

In the structure shown in Figure 4, the arms 59' and til are relatively short members while a single operating lever, as 65, is connected with one of the arms for first effecting release of the brake and afterward rotation in unison of the brake disks 6% and 4t and the actuating members A l and 52. The lever 65 in the structure shown in Figure 4 is pivotally connected as at 66 to the arm Gil and has a ball El or other suitable handle means mounted at the outer end thereof. A tie rod 68 secured to the lever 65 extends laterally therefrom through aligned openings 69 formed in the arms 59 and 66' adjacent the outer end thereof. The rod 68 is provided with a head it at the outer end thereof which, when the brake disks are in holding engagement with their respective braking surfaces, is spaced a slight distance from the outer side of the arm 59', A spring l2 may be connected with the arms 59' and ti! for normally urging said arms toward each other and disengaging the brake. A wedge or cam member 76 mounted on a stern i5 is adapted to engage inwardly projecting contact elements 1S and ii provided on the arms for forcing the arms outwardly away from each other against the action of spring 12. The stem 15 extends, in this case, upwardly through a suitable aperture 78 provided in the rod 58 and has the upper end arm 19 pivoted intermediate its ends, as at 80, to the lever 65. The other end of the arm 19 is pivotally connected with a link 8i which extends upwardly therefrom and has its upper end pivotally connected at 82 to the ball or handle 61.

A spring 83 may, as shown, be positioned at the inner end of a bore 84 provided in the ball 61 for slidably receiving the upper end of lever 65 therein. The spring 83 is tensioned to normally urge the ball til outwardly or upwardly with respect to the lever 65 and thereby urges the cam or wedge member M downwardly between the contact elements 76 and 11.

When it is desired to actuate the brake disk 45 of this structure, it is necessary to first move the ball or handle 61 downwardly or inwardly with respect to the lever 65 thereby moving the Wedge or cam Hi from between the contact elements l6 and ii. This releases the arm members 58 and Si? and permits the spring 72 to move said arms toward each other for disengaging the brake. The brake disk 45 may now be moved in either direction by rocking the lever 65 in a corresponding direction. It will be observed that the spring 12 may be dispensed with, in which case the spring 83 acting through the ball 61 and linkage members Bl, l9 and i5 and cam '54 forces the arms 59 and BE? away from each other for engaging the clutch. If the spring 12 is not used, the operation of the device will be substantially the same as when said spring is used with the exception that during initial swinging movement of the lever 85, after the cam member It has been moved upwardly out of engagement with the contact elements it and W, the arms 59 and Eli will be moved toward each other to disengage the brake and then continued swinging movement of the lever 65 will produce a corresponding rotary movement of the brake disk 65 and the actuating member, such as the pinion 44, connected thereto.

In the structure shown in Figure 5, the operat ing leverage means for releasing the brake and rotating the brake disk 35 is constructed and operated substantially the same as that shown in Figure 4, the primary difierence being that in Figure 5 there is shown a pivoted cam member 54 which is pivotally connected as at $55 with one of the arms, as 5G, while the opposite end of the cam member is adapted to engage the other arm member Ell with a cam action for forcing said arms apart. Furthermore, instead of using a tension spring 72 as in the structure shown in Figure 4, I have shown a compression spring 62' interposed between arms 59' and 66. Spring 62', like spring 62, functions to urge the arms apart and engage the clutch. The operation of the control mechanism shown in Figure 5 is substantially the same as that described above for the structure shown in Figure 4 when the spring F2 is omitted. The handle member 6! is first actuated to move cam id out of engagement with the arm 5Q. Lever G5 is then swung in the desired direction. During the initial movement of lever 85, arms as and ti are moved toward each other against the action of spring E2 to release the brake, after which brake disk t5 and the actuating member dd connected thereto move in unison with the lever mechanism.

In the structure shown in Figure 6, the operat" ing lever, as 65', is pivotally connected at 85 to the brake disk 55 intermediate the arms 59 and 6d. The lever 65 is operatively connected with the arms 59' and lit by a pair of headed links -89,

thereof pivotally connected to one end of a rock These links are pivotally connected -at"90to the lever and extend loosely through suitable apertures 9| provided in the outer ends of the arms 59' and 60' respectively. A spring 92 may be, as shown, interposed between the arms 59' and 60' for normally urging said arms apart and maintaining the brake in the engaged position. In operation, swing ng movement of the lever 55 transmits motion through one or the other of the links 89 to the arm 59 or 60' depending upon the direction in which the lever 65 is moved. When the head 89 of one of the links 89 is brought by this swinging movement of the lever 65 into engagement with the corresponding arm, said arm will be moved toward the other arm and thereby release the brake, after which the brake disk 45 may be rotated by continued swinging movement of the lever 55'.

In the structure shown in Figures 7 and 8, the

end of the screw shaft 52 adjacent the brake disk 45 has an arm 95 secured thereto. This arm carries a pin 96 adjacent the outer end thereof which projects outwardly from the arm into an elongated slot 97 provided in a laterally disposed lug 98 formed at one side of an operating lever 95 mounted on the shaft 52 adjacent the outer face of the arm 95. The lever 99 is maintained on the shaft 52 against axial movement with respect thereto by a collar iii!) secured to said shaft. The lever 95 is provided with an elongated slot or recess I02 which extends longitudinally thereof from Within a short distance of the end of said lever adjacent the shaft 521 upwardly or inwardly. This slot me has the lower portion 12' thereof enlarged to slidably and rotatably receive the adjacent portion of shaft 52 therein. The upper or inner portion I52" of the slot is relatively narrow and slidably receives therein an arm or lug Hi3 secured to or made integral with the brake disk 45. A spring Hi l is mounted in the upper or inner end portion of the slot section "12 intermediate the inner end thereof and the arm I03 for normally urging the lever 99 upwardly or outwardly.

When operating the structure shown in Figures '7 and 8, the lever 99 is first moved downwardly or longitudinally to eifect release of the brake after which the lever may be swung in either direction about the axis of the shaft 52 to rotate the brake disk 45 and the actuating member fi lconnected with said disk. The downward or longitudinal movement of the lever 89 compresses the spring I04 and at the same time rocks the arm 95 due to the engagement of the pin 95 with the lug 98. At the same time the brake disk 45 is maintained against rotation due to the engagement of the arm I53 with the sides of the slot Hill". This rotary movement of arm 95 produces relative rotary movement of the screw shaft 52 and the pinion 44 and thereby moves the brake disk 55 out of clutching engagement with the brake surface 41'. Rocking movement of the lever 59 after the brake is disengaged produces a positive rotary movement of the brake disk 45, irrespective of the direction in which the lever 99 is rocked. As soon as the brake disk 45 and the operating member associated therewith have been moved to the desired position and said lever is released, spring ma forces the lever 99 longitudinally or outwardly with respect to disk 45, thereby producing relative rotary movement of the shaft 52 and pinion 45 by rocking the arm 95 upwardly toward the arm N33. The engagement of the brake disks 45 and 46 with their respective braking surfaces 47' and 48' limits the upward movement of the arm and maintains the brake in the engaged position.

While I have shown the actuating member connected with the brake disk 45 in the form of a gear or pinion, it will be obvious that a lever or other suitable operating means may be substituted therefor to produce reciprocation of the element to be positioned. Furthermore, it will be obvious that other changes in the form and relation of the parts than those shown in the drawings may be readily made, and that my device may be used in conjunction with mechanisms other than lens grinding machines for bringing a machine element into and maintaining it in any selected one of a multiplicity of operating positions. Therefore, I do not wish to be limited to the exact construction and mode of operation shown and described, but only by the structure as claimed.

I claim:

1. A control mechanism of the character described, comprising in combination, a positioning member connected to a machine element for pcsitioning said element, an actuating member oppositely movable in both a first path and a second path, holding means controlled by opposite movements of said actuating member in its first path for respectively holding said actuating member against and releasing it for opposite movements in its second path, said actuating member being connected to said positioning member for moving the latter in responseto movements of said actuating member in its second path, and means operable at will for moving said actuating member back and forth in its first path to release and apply said holding means at any position of said actuating member in its second path and operable when said holding means is released for moving said actuating member back and forth in its second path to change the position at which said positioning member is holdable by application of said holding means.

2. A control mechanism of the characte described, comprising in combination, a positioning member connected to a machine element for positioning said element, a first actuating member and a second actuating member constructed to have relative movement back and forth in a first path and movement in unison back and forth in a second path, holding means effective upon said first actuating member and constructed to be applied and released in response to back and forth elative movements of said actuating members in said first path, said first actuating member being connected to said positioning member for moving the latter in response to back and forth movements in unison of said actuating members in'said second path, and manually con trolled means operable at will for producing relative movement of said actuating members in said first path to apply and release said holding means at any position of said actuating members in said second path and operable when said holding means is released for producing movement in unison of said actuating members in said second path to change the position at which said positioning member is holdable by application of said holding means.

3. A control mechanism for adjustably positioning and releasably maintaining a machine element in a desired operating position against back pressure exerted on said machine element, comprising in combination, a positioning member connected to said machine element for positioning said element, a friction brake including two brake members relatively movable toward and away from each other respectively to apply and release said brake, two brake actuating members connected one to each of said brake members, said brake actuating members being connected together for relative movement in opposed brake-applying and brake-releasing directions, a connection between one of said brake actuating members and said positioning member so constructed. and arranged that movement of said positioning member due to back pressure of said machine element thereon tends to produce relative movement of said brake actuating members in the brake-applying direction, said brake actuating members being so constructed and arranged that they are free to move in unison when said brake is released, and manually controlled means including two relatively movable members connected one to each of said brake actuating members operable at will for applying and releasing said brake and operable when said brake is released for moving said brake actuating members in unison to change the position at which said positioning member is holdable by application of said brake.

4. A control mechanism for adjustably positioning and releasably maintaining a machine element in a desired operating position against back pressure exerted on said machine element, comprising in combination, a positioning ll ember connected to said machine element for positioning said element, a friction brake including two brake members relatively movable toward and away from each other respectively to apply and release said brake, two brake actuating members connected one to each of said brake members, said brake actuating members being connected together for relative movement in opposed brake-applying and brake-releasing directions, a connection between one of said brake actuating members and said positioning member so constructed and arranged that movement of said positioning member due to back pressure of said machine element thereon tends to produce relative movement of said brake actuating members in the brake-applying direction, said brake actuating members being so constructed and arranged that they are free to move in unison when said brake is released, means for normally urging said brake actuating members toward relative movement in the brake-applying direction, and manually controlled means for rendering said last named means temporarily inefiective and for thereafter moving said brake actuating members in unison, whereby the movement of the one of said brake actuating members connected to said positioning member serves to move the latter and change the position at which said positioning member is holdable by application of said brake.

5. A control mechanism for adjustably positioning and releasably maintaining a machine element in a desired operating position against back pressure exerted on said machine element, comprising in combination, a positioning member connected to said machine element for positioning said element, a friction brake including two brake members relatively movable toward and away from each other respectively to apply and release said brake, two brake actuating members connected one to each of said brake members, said brake actuating members being connected together for relative movement in opposed brake-applying and brake-releasing directions, a connection between one of said brake actuating members and said positioning member so constructed and arranged that movement of said positioning member due to back pressure of said machine element thereon tends to produce relative movement of said brake actuating members in the brake-applying direction, said brake actuating members being so constructed and arranged that they are free to move in unison when said brake is released, a pair of arms connected one to each of said brake actuating members for moving the same, means for normally urging said arms in the brake applying direction, and manually controlled means for rendering said last named means temporarily ineffective and moving said arms in the brake releasing direction and for thereafter moving said arms in unison, whereby the movement of the one of said arms which is connected to the brake actuating member connected to said positioning member serves to move the latter and change the position at which said positioning member is holdable by a plication of said brake.

6. A control mechanism for adjustably positioning and releasably maintaining a machine element in a desired operating position against back pressure exerted on said machine element, comprising in combination, a positioning member connected to said machine element to position said element, a friction brake including two brake members relatively movable toward and away from each other respectively to apply and release said brake, two brake actuating members connected one to each of said brake members, said brake actuating members having engaging cam faces and being constructed for applying said brake upon relative rotation in one direction and for releasing said brake upon relative rotation in the opposite direction, a connection between one or" said brake actuating members and said positioning member so constructed and arranged that movement of said positioning member due to back pressure of said machine element thereon tends to produce relative rotation of said brake actuating members in the brake applying direction, said brake actuating members being so constructed and arranged that they are free to rotate in unison in either direction when said brake i released, means for normally urging said brake actuating members toward relative rotation in the brake applying direction, and manually controlled means for rendering said last named means temporarily inefiective and for thereafter rotating said brake actuating members in unison, whereby the movement of the one of said brake actuating members connected to said positioning member serves to move the latter and change the position at which said positioning member is holdable by application of said brake.

'7. A control mechanism for adjustably positioning and releasably maintaining a machine element in a desired operating position against back pressure exerted on said machine element, comprising in combination, a positioning member connected to said machine element to position said element, a friction brake including two brake members relatively movable toward and away from each other respectively to apply and release said brake, two brake actuating members connected one to each of said brake members, said brake actuating members having engaging cam faces and being constructed for applying said brake upon relative rotation in one direction and for releasing said brake upon relative rotation in the opposite direction, a connection between one of said brake actuating members and said positioning member so constructed and arranged that movement of said positioning member due to back pressure of said machine element thereon tends to produce relative rotation of said brake actuating members in the brake applying direction; said brake actuating members being so constructed and arranged that they. are free to rotate in unison in either direction when said brake is released, a pair of arms connected one to each of said brake actuating members for rotating the same, means for normally urging said arms in the brake applying direction, and manually controlled means for rendering said last named means temporarily ineffective and moving said arms in the brake releasing direction and for thereafter moving said arms in unison, whereby the movement of the one of said arms which is connected to the brake actuating member connected to said positioning member serves to move the latter and change the position at which said positioning member is holdable by application of said brake.

8. A control mechanism for adjustably positioning and releasably maintaining a machine element in a desired operating position against back pressure exerted on said machine element, comprising in combination, a positioning member connected to said machine element for positioning said element, a friction brake including two brake disks axially movable relative to one another to apply and release said brake, two brake actuating members connected one to each of said brake disks, said brake actuating members having engaging cam faces and being constructed for applying said brake upon relative rotation in one direction and for releasing said brake upon relative rotation in the opposite direction, a connection between one of said brake actuating members and said positioning member so constructed and arranged that movement of said positioning member due to back pressure of said machine element thereon tends to produce relative rotation of said brake actuating members in the brake applying direction, said brake actuating members and said brake disks being so constructed and arranged that they are free to rotate in unison in either direction when said brake is released, means for normally urging said brake actuating members toward relative rotation in the brake applying direction, and

manually controlled means for rendering said last named means temporarily ineffective and for thereafter rotating said brake actuating members in unison, whereby the movement of the one of said brake actuating members connected to said positioning member serves to move the latter and change the position at which said positioning member is holdable by application of said brake.

9. A control mechanism for adjustably positioning and releasably maintaining a machine element in a desired operating position against back pressure exerted on said machine element, comprising in combination, a positioning member connected to said machine element for positioning said element, a, friction brake including two brake disks axially movable relative to one another to apply and release aid brake, two brake actuating members connected one to each of said brake disks, said brake actuating members having engaging cam faces and being constructed for applying said brake upon relative rotation in one direction and for releasing said brake upon relative rotation in the opposite direction, a connection between one of said brake actuating members and said positioning member so constructed and arranged that movement of said positioning member due to back pressure of said machine element thereon tends to produce relative rotation of said brake actuating members in the brake applying direction, said brake actuating members and said brake disks being so constructed and arranged that they are free to rotate in unison in either direction when said brake is released, a pair of arms connected one to each of said brake actuating members for rotating the same, mean for normally urging said arms in the brake applying direction, and manually controlled means for rendering said last named means temporarily ineffective and moving said arms in the brake releasing direction and for thereafter moving said arms in unison, whereby the movement of the one of said arms which is connected to the brake actuating member connected to said positioning member serves to move the latter and change the position at which said positioning member is holdable by application of said brake.

ELI M. LONG. 

